Mine are far older than 5 years. lol...Maybe 20 ? It's all my fault.
Dang that's a great point though.......I store mine in a non-climate controlled shed but they are inside and out of direct sun. My LW is probably 25 years old and I have been through 2 belts and the 3rd is on it now. None really showed wear but I was well over the 5 years each time so what the heck I replaced them for peace of mind....they were like under 40 each time.
There was a thread here not long ago where a guy was saying his belt only lasted like 3 years (I think) and rotted away.....said he kept it indoors and everything!? Makes me wonder if it's not something like the light, heat or whatever like you are saying. ??? Maybe different manufacturers or sub-contractors?
I work for a really large company and we get parts in for years and then BAM we get garbage that doesn't work......each time that happens we find out they had to get parts from another vendor.......either to save a dime or because of support issues.
The old belts were not grey but transparent honey colored so I know for sure they have changed at least once. I hope they come out soon with them or maybe I'll start a small business..............lol